Body formed of set, initially pasty material and including an electrically conducting path and a method of making such a body

ABSTRACT

A body ( 5 ) of set, initially pasty material, such as concrete, includes an electrically conducting path formed by a concentrated layer ( 6 ) of electrically conducting magnetizable elements, such as fibers (F) or granules (G), embedded in the initially pasty material and extending through at least a portion of the body ( 5 ). Electrically conducting terminal members ( 9 ) may be connected to the electrically conducting layer ( 6 ) at spaced-apart positions along the layer ( 6 ). A method of providing such a body ( 5 ) includes the steps of: (a) forming a body of the pasty material in which electrically conducting magnetizable elements (F) are dispersed, (b) applying a magnetic field to the body of pasty material to form from the magnetizable elements an electrically conducting layer embedded in the body of pasty material and extending at least through a portion the body ( 5 ), and (c) causing the body of pasty material containing the layer ( 6 ) to set. Before or after the setting of the body ( 5 ) of pasty material, electrically conducting terminal members ( 9 ), may be connected to the electrically conducting layer ( 6 ) at spaced-apart positions along the layer.

This invention relates to a body formed of a set, initially pastymaterial and including an electrically conducting path. Moreover, theinvention relates to a method of making such a body.

It is known to reinforce bodies of concrete or other cementitious andinitially pasty, viscous material by including steel or carbon fibres inthe concrete or other pasty material before it is allowed to set. In thecase of concrete and where the fibres are of steel, they typically havea length of 2.5 to 8 cm or longer and a diameter in the range of 0.5 to1 mm and thus are relatively rigid. During the mixing of the fibres andthe concrete, the fibres are dispersed in the concrete and orientatedrandomly in three dimensions so that the cast and hardened concrete bodywill be reinforced in three dimensions.

Many, or even most, concrete structures are only stressed in one or twodimensions, however, so that reinforcement in one or two dimensionswould be adequate. This is so in the case of concrete floor slabs andconcrete road pavements, to mention only two examples.

According to a known method for one-dimensional alignment of steelfibres in slabs of wet concrete newly cast in a form, a magnetic fieldis directed through the newly cast, wet concrete body in the castingform and displaced relative to the form from one end or side thereof tothe other in order to apply a temporary aligning force to the individualfibres for aligning them in the direction of relative movement (U.S.Pat. No. 4,062,913). To facilitate the aligning movement of the fibresunder the action of the magnetic field, the concrete body is vibratedduring the relative movement of the magnetic field and the concretebody.

It has been proposed to use electrically conducting fibres in concreteto pass an electric current through the concrete for heating or otherpurposes, e.g. to provide electrical earthing or electromagneticshielding (U.S. Pat. Nos. 5,346,547, 5,447,564, EP-A-0449439.

However, conducting fibres which are randomly orientated orone-dimensionally aligned by the known technique are not suitable forsuch purposes, because they do not provide a suitable electricallyconducting path through the concrete and because it is difficult toobtain a satisfactory connection of electrical terminal members to thefibres. The concrete itself is a poor conductor and the fibres aresubstantially evenly distributed throughout the concrete so that onlyfew fibres contact each other. For that reason, the fibres do notprovide a coherent and wide current path between the terminal members.

An object of the invention is to provide an improved body of the kindindicated above. A further object is to provide a method of making sucha body.

In accordance with the present invention there is provided body formedof a set, initially pasty material and including an electricallyconducting path formed by a concentrated layer of electricallyconducting magnetizable fibrous and/or granular elements, said layerbeing embedded in said material and extending through at least a portionof said body.

Because the initially more or less randomly distributed magnetizablefibrous and/or granular elements in the pasty material, which may beconcrete, for example, are ultimately stratified to form a layer inwhich they are substantially more densely arranged than initially, asufficiently large number of fibres or granular elements aresufficiently close or contact one another throughout the extent of thelayer to provide between the terminal members a conducting path ofadequate current carrying or shielding capability. Preferably, the layeris positioned such that that it extends generally parallel to a face ofthe body, which may be, for example a slab or some other plate-likebody. If the body is to be used in an application in which it isdesirable to pass an electric current through the electricallyconducting path formed of or including the layer, e.g. to heat the body,the body preferably includes electrically conducting terminal membersconnected to the electrically conducting layer at spaced-apart positionsalong the layer.

If the layer of magnetizable elements is made up of or includesreinforcing fibres of metal, it suitably is positioned in the body wherethe demand for reinforcement is the greatest. The thinning out of thefibre reinforcement in other parts of the body resulting from theconcentration of the fibres to a single or a few layers therefore neednot entail any serious loss of the strength of the body.

In accordance with the invention there is also provided a method ofproviding an electrically conducting path in a body formed of a set,initially pasty material, the method including the steps of forming abody of the pasty material in which electrically conducting magnetizablefibrous or granular elements are dispersed, applying a magnetic field tothe body of pasty material to form from the said magnetizable elementsan electrically conducting layer embedded in said body of pasty materialand extending at least through a portion thereof, causing said body ofpasty material containing said layer to set, and connecting electricallyconducting terminal members to said electrically conducting layer atspaced-apart positions along the layer.

Aggregate in the form of granular iron ore (magnetite) or othermagnetizable granular material having some electrical conductivity mayform the layer alone or, preferably, together with magnetizable metalfibres. In the latter case, the conducting granular material will reducethe resistivity of the portions of the initially pasty materialseparating the fibres.

The stratification of the magnetizable fibrous and/or granular elementsby magnetic means in accordance with the method of the invention may becarried out by the method and the device for stratifying and aligningmagnetizable metal fibres which are described and claimed inInternational Application PCT/SE99/01150, published as WO99/67072.

As described in the above-identified international application, themagnetic stratification and alignment of magnetizable fibres dispersedin a viscous or pasty body is carried out by means of a stratifyingmember having a nonmagnetic wall. A magnetic field is directed into theviscous body through a first portion of the nonmagnetic wall while thefibre-stratifying member is being moved relative to the body of pastymaterial with the nonmagnetic wall contacting the body and with a secondportion of the nonmagnetic portion trailing the first portion.Accordingly, the fibres are temporarily subjected to the magnetic fieldas the first portion moves past them.

The fibre-stratifying member may be partially or completely immersed inthe pasty material as it is moved relative to the body with the firstportion of the magnetic wall ahead of the second portion and thustrailed by the latter.

During the relative moment, the fibres in the vicinity of the firstportion of the nonmagnetic wall are magnetically attracted towards thefirst portion. However, they are prevented from coming into contact withthe magnetic device by the nonmagnetic wall, which forms a screen orbarrier that separates the magnet device from the pasty material inwhich the fibres are dispersed.

The fibre-stratifying member therefore attracts the fibres and tends topull them along in the direction of its movement relative to the body ofpasty material. Because of its viscosity or pasty character, thematerial of the body prevents the fibres from moving too rapidly towardsthe stratifying member and sticking to it. Thus, the fibre-stratifyingmember will move relative to the fibres and subject them to the magneticforce only temporarily. Since the magnetic force has a component in thedirection of relative moment of the fibre-stratifying member and thepasty body, it not only will draw the fibres towards thefibre-stratifying member and thus stratify them to form a densifiedfibre layer within the body, but also tends to align the fibres in thatdirection as it moves past them.

Preferably, the pasty material containing the fibres is vibratedadjacent the fibre-stratifying member so that the stratifying andaligning movement of the fibres is facilitated.

The terminal members may be connected to the conducting layer formed bythe densified layer of fibres or other magnetizable conducting elementsin any suitable manner, before or after the pasty material has set. Forexample, the concrete or other pasty material may be locally removed toexpose the conducting layer in a narrow groove extending across thelayer, whereupon a braided strip of copper wire or some other suitableform of “bus bar” conductor adapted for connection to an electric powersource, is placed across the layer and secured to it by pouring moltentin over the strip and the exposed layer.

The invention will be more fully understood from the followingdescription with reference to the accompanying drawings showingapplication of the invention to the production of pavements or otherslabs of concrete cast on the ground.

FIG. 1 is a diagrammatic perspective view illustrating the basicprinciple of the invention as applied to a concrete slab having anelectrically conducting path formed from a concentrated layer ofmagnetizable reinforcing fibres;

FIG. 1A is an enlarged perspective view of a corner of the slab shown inFIG. 1;

FIG. 2 is an overview illustration showing successive steps in theproduction of a concrete pavement on the ground, one of the steps beingthe formation of a concentrated layer of reinforcing steel fibres inaccordance with the invention;

FIG. 3 is a perspective view of a fibre-stratifying device used in thestep shown in FIG. 2;

FIG. 4 is a cross-sectional view of the section of the concrete pavementof FIG. 2 in which the fibre stratification is being carried out;

FIGS. 5–7 are diagrammatic views of three slabs of different heightscast on the ground and shown together with fibre-stratifying devices;

FIG. 8 is a cross-sectional view showing a modification of the device ofFIG. 7;

FIG. 9 is a cross-sectional view showing a modification of thefibre-stratifying device of FIG. 4.

FIGS. 1 and 1A show a rectangular flat concrete body 5, a slab, which isreinforced by means of a multiplicity of magnetizable metal fibresembedded in the concrete and included in a concentrated layer 6 ofdensely packed fibres F. This layer extends from one end 7 of theconcrete body to the other end 8 and is positioned between and parallelto the large faces of the concrete body 5. Two electrically conductingterminal members 9 are embedded in the concrete in contact with fibresof the layer 6 near the ends 7, 8 of the body 5 to pass an electriccurrent provided by a current source 10 into and out of the body throughthe fibre layer 6. A multiplicity of particulate bodies G of anelectrically conducting material, such as iron ore (magnetite), formingpart of the aggregate of the concrete may be included in the layer 6 toenhance the electrical conductivity of the layer.

The concrete constituting the main mass of the body 5 may be anyconventional concrete including conventional aggregate. Similarly,although steel fibres of the kind commonly used for reinforcing concreteare normally preferred, the fibres may be any magnetizable fibres havingthe desired electrical conductivity.

As shown by way of example in FIG. 2, the invention is applied to theproduction of a concrete pavement or slab on the ground. The pavement isshown at different successive steps during its production, the firststep being shown to the left and the last step being shown to the right.Furthest to the left, at A, the wet concrete is cast after reinforcementfibres of steel or some other magnetizable material has been added tothe concrete and uniformly dispersed in it with random orientation.Then, at B, the wet concrete is vibrated and the reinforcing fibres arealigned lengthways and stratified to form a horizontal layer embedded inthe concrete, using a fibre-stratifying device 11 embodying theinvention. The fibre-stratifying device 11 is supported by and slidableon rails 12 positioned along the longitudinal edges of the pavement. AtC the wet concrete with the stratified and aligned fibres is vacuumtreated, and at D the pavement is smoothed.

The fibre-stratifying device 11 comprises a horizontal main beam 13extending across the strip of ground to be paved and resting on therails 12. It is manually displaced and controlled by means of controlrods 14 with handlebars.

A straight horizontal fibre-stratifying member 15 in the shape of a beamor bar is suspended from the main beam 13 by means of hangers 16 whichare vertically adjustable to permit positioning of the stratifyingmember 15 at a selected height. The stratifying member 15 extends acrossthe entire space between the rails 12.

An elongate housing or shell 17 forming part of the stratifying member15 is drop-shaped in cross-section so that it resembles an airfoil, therounded first or leading edge of which is directed such that it will beforemost when the stratifying device 11 with the stratifying member 15is displaced in the proper direction, to the left in FIG. 1, during thestratifying operation. This housing 17 is made of aluminium or someother suitable nonmagnetic material.

Inside the housing 17 of the stratifying member 15, along a foremost orfirst wall portion 17A of the housing, a rotatably journalled magnetroll 18 extends along the entire length of the stratifying member 15.The first portion 17A of the wall of the housing is arcuate incross-section and the axis L of the magnet roll 18 coincides with theaxis of the first wall portion 17A.

Three permanent magnets 19, made of neodym, for example, are uniformlydistributed about the magnet roll 18, each such magnet subtending about⅙ of the circumference of the magnet roll. The outer surfaces of themagnets 19 are positioned on a circular cylindrical surface concentricwith and closely spaced from the first portion 17A of the wall of thehousing 17. When the magnet roll 18 is caused to rotate as describedbelow, the permanent magnets 19 accordingly will move close to the innerside of the first wall portion 17A.

As indicated by the north and south pole designations N and S and themagnetic field lines in FIG. 4, the magnets 19 are mounted on the magnetroll 18 such that the field lines run in planes which are perpendicularto the axis L of the magnet roll 18. In the illustrated embodiment themagnet roll 18 is rotated counter-clockwise, viewed as in FIG. 4, by anumber of electric motors 20 spaced apart along the length of thestratifying member 15. If desired or required, the direction of rotationof the magnet roll 18 can be reversible.

To permit adjustment of the stratifying member 15 to a desired angle ofattack, so that the trailing or second portion 17B of the wall of thehousing 17 will be at a selected height, the stratifying member 15 ismounted for pivotal movement about an axis which is parallel to, e.g.coinciding with, the axis L of the roll 18. Locking means, not shown,are provided to lock the stratifying member 15 in a selected angularposition.

During the fibre stratification and aligning operation thefibre-stratifying device 11 rests on the rails 12 with the stratifyingmember 15 set at a height such that the lowermost segment of the firstportion 17A of the wall of the housing 17 is relatively close to theunderside of the cast layer of wet pasty concrete. Moreover, thestratifying member 15 is adjusted angularly such that the second portion17B of the wall of the housing 17 is at approximately the same height asthe lowermost segment of the first wall portion 17A.

After the stratifying member 15 has been adjusted to the desired heightand the desired angular position, the stratifying device 11 is slowlydisplaced to the left as viewed in FIGS. 2–4 so that the first portion17A of the wall of the housing 17 is ahead of and trailed by the secondwall portion 17B. The magnet roll 18 rotates continuously in thedirection indicated by an arrow (counter-clockwise), and a vibrator Vsupported by the stratifying device 11 operates to vibrate the concretein the region of the body of concrete in which the stratifying member 15operates.

As indicated by the outline arrows in FIG. 4, a portion of the concreteis displaced upwards and passes across the upper side of the stratifyingmember 15 while another portion is displaced downwards and passes acrossthe underside. During their movement along the inner side of the leadingfirst wall portion 17A, the permanent magnets 19 provided on the magnetroll 18 will direct their magnetic fields into the concrete in front of,above and below the first wall portion 17A.

The magnetic fields, the field lines of which generally run in planeswhich are perpendicular to the axis L of rotation of the magnet roll 18,orbit counter-clockwise together with the roll. During their orbitingmovement they apply to the reinforcement fibres F subtended by themagnetic fields a magnetic attraction force that tends to attract thefibres towards the leading first wall portion 17A of the housing 17 andto align the fibres along the field line planes. At the same time,fibres positioned above the level of the underside of the stratifyingmember 15 are drawn downwards by the magnetic attraction and thedownward diversion of concrete, and fibres below that level are drawnupwards.

Accordingly, the fibres F, or at least a large proportion of them, tendto move towards the underside of the stratifying member 15 and stratifythere to form a horizontal layer S of densely arranged fibres, a largeproportion of which are aligned predominantly in the relative directionof movement of the stratifying member 15 and the concrete body. Aconsiderable number of fibres F in or close to the layer may also beorientated at an angle to the relative direction of movement to formconducting bridges between laterally separated fibres.

When a fibre F reaches a position abreast of the intermediate flat wallportion 17C of the underside of the housing 17, the strength of themagnetic field, and thus the magnetic attraction on the fibre, decreasessharply because the magnet 19 which is closest to the transition betweenthe first wall portion 17A and the intermediate wall portion 17C movesupwardly away from the fibre. Accordingly, the magnetic attraction onthe fibre F will no longer be strong enough to pull the fibre along withthe stratifying member 15, so that the fibre will be left behind in thealigned position in the fibre layer T.

When a fibre F reaches a position abreast of the intermediate flat wallportion 17C of the underside of the housing 17, the strength of themagnetic field, and thus the magnetic attraction on the fibre, decreasessharply because the magnet 19 which is closest to the transition betweenthe first wall portion 17A and the intermediate wall portion 17C movesupwardly away from the fibre. Accordingly, the magnetic attraction onthe fibre F will no longer be strong enough to pull the fibre along withthe stratifying member 15, so that the fibre will be left behind in thealigned position in the fibre layer S.

FIGS. 5, 6 and 7 diagrammatically show three different ways of carryingout the invention. The technique represented by FIG. 5 essentiallycorresponds to the technique shown in FIGS. 2–4 and described above.Accordingly, the stratification and alignment of the fibres takes placeafter the wet concrete containing the fibres has been placed on theground.

FIGS. 6 and 7 show embodiments in which the stratification and alignmentof the fibres takes place during the placement of the concrete layer onthe ground. More particularly, FIG. 6 shows a device for placing theconcrete and stratifying and aligning the fibres which device isintended to be carried by a laying vehicle moving along the surface onwhich the reinforced concrete body is to be placed. In this device thestratification and alignment of the fibres takes place in two steps. Thewet concrete with admixed reinforcing fibres is fed into a steeplyinclined bin 21 in which two stratifying members 22 similar to thestratifying member 15 of FIGS. 2 to 4 are positioned side by side. Anadditional stratifying member 22 similar to the stratifying member 15 ispositioned in a laying nozzle 23. This nozzle forms a downwardcontinuation of the bin 21 and has a spout with a straight dischargeopening through which a layer of concrete of the desired thickness isdischarged and placed on the ground.

The device shown in FIG. 7 is primarily intended to be used for layingof relatively thin and narrow layers and is manipulated manually. Itincludes a laying nozzle 24 resembling the laying nozzle 23 in FIG. 6and a tubular shaft 25 into which wet concrete with admixed fibres isfed from a concrete pump (not shown) through a hose. Within the layingnozzle 24 a stratifying member 26 similar to the stratifying member 15of FIGS. 2 to 4 is disposed. FIG. 8 shows the device in FIG. 7 ingreater detail.

FIG. 9 shows a modification of the stratifying member 15 of FIGS. 2 to4. In this case there is provided inside the rotatable magnet roll 18′ astationary second magnet roll 27 which is positioned in the rear regionof the first or leading portion 17A of the wall of the housing 17. It isarranged in operation to rotate at a speed which has a certain numericalrelationship, 3:1, to the speed at which the magnet roll 18′ rotates.One half of the magnet roll 27 is magnetized as indicated by the poledesignations N and S while the other half is substantially unmagnetized.Whenever one of the permanent magnets 19 of the rotating magnet roll 18enters the region in which the magnet roll 27 is positioned, themagnetic field of that magnet 19 will close its field lines through themagnet roll 27 so that only a small portion of the magnetic field isdirected into the concrete body. Consequently, the attraction the magnetroll 18′ exerts on the reinforcing fibres in the concrete body, and thusthe tendency of the stratifying member 15 to pull the fibres along, isvery sharply reduced when the fibres are in the region beneath themagnet roll 27.

Several modifications of the presently preferred stratifying method anddevice shown in the drawings are possible within the scope of theinvention as defined in the claims.

For example, the cross-section of the housing 17 of the stratifyingmember 15 may be substantially symmetrical with respect to a plane thatpasses through the axis L of the magnet roll 18 and is substantiallyperpendicular to another plane that passes through the axis L and theedge of the second portion 17B of the wall of the housing 17. With thissymmetrical cross-section, the stratifying member accordingly has a thinedge portion on opposite sides of the thickest section of the housing 17where the magnet roll 18 is positioned so that it can be moved inopposite directions in the concrete, e.g. across the width of a widepavement strip, without encountering a great resistance to the movement.

In this modification, it may be preferable to have two magnet rolls 18,which are associated with opposite sides of the housing 17 and rotate inopposite directions. Alternatively, a single magnet roll 18 may beprovided which has only a single magnet on the circumference and isrotated alternately in opposite directions through an angle of more than180 degrees and preferably approximately 270 degrees. The magnetic fieldwill then be directed alternately into the concrete above thestratifying member and into the concrete below the stratifying member.This mode of intermittent, reversed rotation ensures that the fibres aretemporarily subjected to a magnetic pulling force in the direction inwhich the stratifying member 15 moves relative to the concrete.

Although in the embodiment of the invention described and illustrated inthe drawings a large majority of the stratified fibres are alignedhorizontally generally in the direction of relative movement of thestratifying member and the concrete, it is possible to align the fibresin a horizontal direction generally perpendicular to the direction ofrelative movement if the magnets 19 on the magnet roll 18 are magnetizedsuch that their magnetic field lines run predominantly in planesextending along the length of the stratifying member 15. By suitablymatching the speed of relative movement to the strength of the magnetsand the viscosity of the wet concrete, it is also possible to have anincomplete alignment of the fibres in the direction of the relativemovement so that a fairly large number of fibres extend at a smaller orlarger angle to the direction of movement. Thereby a reinforcement inthe transverse direction is obtained and at the same time the number ofcontact points between the fibres is increased.

It is also to be noted that the magnets or other means producing themagnetic fields, or all such magnets or other means, need notnecessarily be movable relative to the stratifying member. Fixedpermanent magnets or other devices producing magnetic fields may beincorporated in the stratifying member to direct constant orintermittent magnetic fields into the material containing themagnetizable fibres to stratify and align them.

1. A solid body formed of a set, initially pasty cementitious materialand including an electrically conducting path formed by a concentratedlayer of electrically conducting magnetizable fibrous and/or granularelements, said layer being embedded in said material and extendingthrough generally parallel to a face of said body.
 2. A body accordingto claim 1 in which electrically conducting terminal members areconnected to said electrically conducting layer at spaced-apartpositions along the layer.
 3. A body according to claim 1 in the shapeof a slab, said concentrated layer of electrically conductingmagnetizable elements extending generally along a face of the slab.
 4. Abody according to claim 1 in which the said concentrated layer ofelectrically conducting magnetizable elements includes granular ironore.
 5. A body according to claim 2 in which the major portion of eachof the electrically conducting terminal members is embedded in the body.6. A body according to claim 1 in which the electrically conductingmagnetizable elements include fibres which are aligned in said body toextend generally in the direction of a line extending betweenspaced-apart positions along the layer.
 7. A body according to claim 1in which steel fibres are included in said layer.
 8. A method ofproviding an electrically conducting path in a body of a set, initiallypasty cementitious material, including the steps of forming a body ofthe pasty material in which electrically conducting magnetizable fibrousand/or granular elements are dispersed, applying a magnetic field to thebody of pasty material to form from the said magnetizable elements anelectrically conducting layer embedded in said body of pasty materialand extending extending generally parallel to a face of said body ofpasty material, and causing said body of pasty material containing saidlayer to set.
 9. A method according to claim 8, further including thestep of connecting electrically conducting terminal members to saidelectrically conducting layer at spaced-apart positions along the layer.10. A method according to claim 8 in which the pasty material includesgranular iron ore bodies initially distributed substantially uniformlyin the pasty material.
 11. A method according to claim 8 in which thebody of pasty material is a slab.
 12. A method according to claim 8 inwhich the electrically conducting layer is formed by movement of astratifying member including magnet means for producing said magneticfield, said movement being substantially parallel to a face of the bodyof pasty material.
 13. A method according to claim 12 in which thestratifying member is at least partially immersed in the body of pastymaterial during said movement.
 14. A method according to claim 12 inwhich the body of pasty material is vibrated during said movement of thestratifying member.
 15. A method according to claim 12 in which themagnetic field is applied to the body of pasty material predominantlythrough a non-magnetic wall of the stratifying member.
 16. A methodaccording to claim 15 in which the magnetic field is applied to the bodyof pasty material substantially exclusively through said nonmagneticwall.
 17. A method according to claim 12 in which the field lines if themagnetic field applied to the body of pasty material run predominantlyin planes which are substantially transverse to said face of the bodyand substantially parallel to the direction of said movement of thestratifying member.
 18. A method according to claim 15 in which themagnetic field is directed into the body of pasty material by means of amagnet means which is enclosed in the stratifying member and causedduring said movement of the stratifying member to move angularly aboutan axis extending generally parallel to said face of the body of pastymaterial and transverse to the direction of said movement of thestratifying member.
 19. The solid body of claim 1, wherein theelectrically conducting path is in a plane parallel to a longitudinalplane of said body.
 20. The method of claim 8 wherein the electricallyconducting layer is in a plane parallel to a longitudinal plane of saidbody.